Disclosed herein is a seat cushion and a vehicle seat, and particularly, a seat cushion and a vehicle seat that easily follow a contour of an occupant's body, have satisfactory vibration characteristics, and provide an excellent sitting comfort.
Generally, in a vehicle seat, a seat portion (seat cushion) supporting the buttocks and thighs of an occupant is provided in a manner that a cushion pad is placed on a seat base frame and is covered with a skin material (trim cover). In such a seat cushion, various structures have been proposed in order to provide a satisfactory sitting comfort for the occupant.
As a factor that influences the sitting comfort, the contour following capability (fit comfort) of the seat cushion with respect to the occupant or the vibration characteristics in the vehicle running state may be exemplified. In particular, the vibration characteristics may easily influence the occupant sitting on the seat cushion for a long period of time.
In a vehicle such as an automobile or an electrical train, a vibration is generated from a floor surface in a vehicle running state. When the vibration generated at this time is transmitted to the vehicle seat, the seat cushion is vibrated at a low frequency (about 3 to 4 Hz). As a result, since the occupant's body resonates with the seat cushion, the sitting comfort may be degraded.
To address this, as a technique of reducing a vibration in a low-frequency bandwidth generated by the seat cushion in the vehicle running state and hence ensuring a satisfactory sitting comfort of the seat cushion, a technique of providing a seat suspension device is proposed, but there is a problem of complex structure and size increase.
As a technique of ensuring the satisfactory sitting comfort of the seat cushion, for example, a technique is known which reduces a vibration transmitted from a vehicle body and reduces a resonance. In such a technique, specifically, a seat cushion may be exemplified in which a pan frame is provided and a plurality of S-shaped springs are installed at positions corresponding to the buttocks of the occupant in the pan frame. When the seat cushion has the above-described configuration, a satisfactory cushion property may be obtained by the elastic deformation of the S-shaped springs and the cushion pad. As a result, it is possible to reduce the vibration transmitted from the vehicle body in the vehicle running state.
Regarding the seat cushion having a configuration in which such a pan frame is provided with the S-shaped springs, Japanese Patent Document No. 1997(H09)-117346 A (“the '346 Document”) discloses a seat cushion which further reduces a vibration. In the seat cushion disclosed in the '346 Document, a seat cushion is disclosed in which a recessed buttocks receiving portion (air room) is formed in a pan frame at a position corresponding to the buttocks of the occupant. In the seat cushion, the air room is a space which is formed between the pan frame and a cushion pad (described as a “seat pad” in the '346 Document) placed on the pan frame, and an orifice communicating with the air room is formed in a wall surface of the pan frame.
By the above-described configuration, in the seat cushion disclosed in the '346 Document, air satisfactorily flows out of the air room with the compressive deformation of the cushion pad, and hence the seat cushion itself may reduce the vibration.
Further, as a technique involved with the seat cushion having a satisfactory sitting comfort, a technique of reducing a sitting pressure at a specific position influencing a sitting comfort is disclosed in Japanese Patent Document No 2004-255208 A (“the '208 Document”).
In the seat cushion (described as a “sitting pressure reduction seat” in the '208 Document) disclosed in the '208 Document, a hole or a concave portion is formed directly below an ischial tuberosity of an occupant in a pan frame to decrease the pressure directly below the ischial tuberosity (the pressure of the portion with the highest sitting pressure).
In the seat cushion disclosed in the '346 Document, since the S-shaped springs are installed in the pan frame to be located at the positions corresponding to the buttocks of the occupant, the cushion pad may easily follow the human body contour of the occupant. Then, since the S-shaped springs are installed above the air room, the vibration may be reduced without separately providing the suspension device or the like.
However, in the seat cushion of the '346 Document, the pan frame as the seat base frame is provided in the entire surface of the seat base frame, and the pan frame needs to be disposed to the portion corresponding to not only the thighs of the occupant but also the buttocks thereof. As a result, a problem arises that the weight is large. Accordingly, it is desirable to devise a seat cushion which further improves a sitting comfort by a simple and light-weight configuration of the seat cushion and high contour following capability to an occupant.
Further, in the '208 Document, since the cushion pad (described as a “cushion member” in the '208 Document) is placed on the pan frame provided with the hole or the concave portion, the sitting pressure (the ischial pressure) is reduced. However, since the upward biasing force is not exerted when the cushion pad is deflected by the load of the occupant, a problem arises that the contour following capability to the occupant's body is not satisfactory.
Accordingly, a technique has been desired which provides a seat cushion that has high contour following capability to an occupant's body (that is, a satisfactory fit comfort), has a low sitting ischial pressure, and has a satisfactory sitting comfort.